[vos-d] SecondLife geometry

[Or Botton]

Sorry for the late reply, just noticed this discussion.

Secondlife supports cutting but no boolean. You can link several  
links together, and position them one inside the other to simulate a  
new surface - but in truth, it will still be a group of separate  
primitives, and no boolean operations are possible. Infact, we've  
been asking for it for awhile.

There are several types of graphics i've spotted in SecondLife:
A terrain bumpmap - for the world's terrain, can be edited via a  
standard raw file.
A poser avatar mesh - The avatars are poser 2 models. We believe they  
messed with the design abit, but thats what they are.
Primitives - pretty much everything else, other then the standard  
issue skybox.
Particles - Clouds, several UI effects, and other effects that can be  
generated via scripted objects.

The physics engine treats all the objects as individual primitives.  
Infact, for this reason, physics-enabled objects have been  
artificially limited to 31 primitives - LL says that too many  
physical objects with more primitives then this can cause the physics  
engine of the local simulator to slow down drastically and possibly  
"deep think" and halt.

Every primitive can stand for itself. Each of them has their own  
personal "inventory" which can contain symlinks to other objects,  
including their own personal instances of script bytecodes - enabling  
each primitive to be individually scripted and have its own  
programmed reaction, including communication with other primitives  
within the same object as they. Most of the complex 3D effects are  
currently achieved by commanding the various primitives to move or  
transform in a certain way to simulate all sorts of motions.  
Commanding the "Root" primitive will cause the entire linked set to  
move in the world itself.

The physics engine is Havoc 1. It is running on the sim, sending  
updates on all objects to connected viewers. Objects will always  
continue the previously given movement and will even clip through  
other objects in the scene unless another command is sent as  
override. (Not very good for games - slow reaction time)

After playing with various streaming 3D clients - from Active Worlds  
to Blaxxun, Plastic Planet, Caligari, Terangreal and even GuildWars  
(Zone art files are only downloaded on demand, when you cross the  
border or enter a building - from that point onward they are  
available on disk), I can safely say that Linden Lab's primitives  
method is pretty good for streaming: It provides the fastest results.

With most systems I had to wait up to several minutes to download a  
complex scene. With SecondLife the wait is limited to 5 seconds at  
best, with everything else finishing to render as you move in about  
30 seconds to a minute even in a very complex scene.

The problem is - SecondLife have not progressed this technology very  
far beyond adding afew features such as new primitive shapes, light  
sources and flexible primitives.

One feature that would be interesting to see would be the ability to  
"fuse" the edges of primitives together to create a skinned object on  
the client side, boolean operations, or even the ability to specify  
"custom" primitive designs. As long as the server see the primitives  
only as such or possibly "nodes", it should be possible to create all  
sort of interesting effects purely client-side to enhance the graphics.

On Jan 11, 2007, at 4:58 AM, Mark Wagner wrote:

> On 1/10/07, Reed Hedges <reed at interreality.org> wrote:
>>
>> Does anyone know if you can do boolean operations with prims?  I  
>> vaguely
>> recall that you can apply a few "cut out" operations but not  
>> completely
>> general prim-prim boolean ops??
>>
>
> You can perform various CSG-like transformations on prims, but
> SecondLIfe does not support CSG.  I suspect that this is because the
> prims are converted into meshes for rendering: CSG on meshes is a
> non-trivial problem.  It may also be related to the physics engine
> they use.
>
> -- 
> Mark Wagner
>
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